1. Field of the Invention
The present invention relates to ball transferring methods and apparatus for transferring balls to form spherical bumps on electrodes of a semiconductor device, a printed circuit board, or the like. In particular provided are techniques for removing excess balls from a ball carrier on which balls being transferred are temporarily arranged.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 7-153765 discloses spherical bump bonding method and apparatus for easily and surely bonding spherical bumps onto electrodes of a semiconductor device, a printed circuit board, or the like.
Japanese Patent Application Laid-open No. 8-112671 discloses a feature that vibration is applied to a suction head with solder balls being carried thereon in order to allow the solder balls to drop off.
In the method disclosed in the former Japanese Patent Application Laid-open No. 7-153765, as shown in FIGS. 1A and 1B for example, an apparatus is used which comprises a ball arranging unit 1, a carrier board conveying mechanism 2, ball inspection means 3, and a bonding stage 4.
In the ball arranging unit 1, as shown in FIG. 2, fine metallic balls B are put in a ball stocking tray 11, which is vibrated with a vibrator 12. The balls B are thereby made to jump effectively and sucked onto ball suction means 13. The ball suction means 13 is provided with a ball carrier board 15 where suction holes 14 each having a diameter smaller than the ball diameter are arranged into a predetermined pattern. The pattern preferably corresponds to the area of two or more semiconductor chips.
The ball suction means 13 is lowered to the vicinity of the ball stocking tray 11 and balls B are sucked onto the respective suction holes 14 of the carrier board 15 by vacuum.
The ball suction means 13 is then lifted up and excess balls B′ other than balls B that have been exactly sucked onto the respective suction holes 14 are removed and collected for reuse. The exactly sucked balls may be referred to as normal balls hereinafter. In the prior art apparatus, a vibrator 16 is used as means for removing the excess balls. The vibrator 16 applies fine vibration to the ball suction means 13 in order that only the excess balls B′ may be removed without removing the normal balls B.
In this manner, the excess balls B′ can be removed so that only one ball B is sucked onto each suction hole 14 of the carrier board 15. This brings about an exact arrangement of the balls B on the carrier board 15 and so shortening of the mass production tact time.
However, if the carrier board 15 has a soil and a excess ball B′ has adhered to the carrier board 15 through the soil, the soil may serve as a buffer between the excess ball B′ and the carrier board 15, so that the vibration is not properly transmitted to the excess ball B′ and the excess ball B′ can not be removed. In this case, application of more intense vibration may result in removal of normal balls B.
For this reason, the carrier board 15 has been cleaned in general. In case of a ball size of less than 300 μm, particularly less than 150 μm, however, even a very small soil or dirt may cause such adhesion of a excess ball B′.
Besides, if too intense vibration is applied upon sucking balls in order to avoid excess ball adhesion, a normal ball B exactly sucked onto a suction hole of the carrier board 15 may rotate as it is being sucked. This may cause damage on the ball surface, which damage leads to an erroneous detection upon optical inspection of the ball arrangement. Besides, if removed excess balls are scattered in the ball transferring apparatus, then it mostly results in a machine trouble.